Tempered Glass Test

Ask any optician how he can tell if a glass for eyeglasses is heat treated--tempered "Safety Glass Law to Affect Escrows" (Aug. 24). He would look at it with a polariscope.

With a glass door you could hold Polaroid eyeglasses on each side and look through and move lenses about at the same time. Sunlight on a thick glass door at a bank, for example, will look like dark areas all over it, about three inches apart.